Among the conventional load sensors, a load sensor as disclosed in the Japanese Patent Laid-open No. 07-174646 is widely known. FIG. 30 shows a perspective view of the conventional load sensor. An elastic board 1 is fixed at four corners to a base 3 with a fixing member 4, and an operating rod 2 made of a rigid material is provided at the center of elastic board 1. When the end of operating rod 2 is given with a force in parallel with the elastic board 1, the elastic board 1 makes a deformation. In the areas between the operating rod 2 and the fixing member 4, a pair of strain detecting elements 5 and 6 are provided respectively on lines connecting the fixing member 4 and the operating rod 2 forming right angles to each other at a same distance from the operating rod 2, totalling two pairs; the first pair of strain detecting elements 5 comprising elements 5A and 5B, while the second pair of strain detecting elements 6 comprising elements 6A and 6B. These elements 5A, 5B, 6A and 6B are strain-responsive resistor elements and have a same value of resistance.
Operation of the load sensor is described referring to FIG. 31. When the operating rod 2 is given at its end with a force in the direction P1 that is parallel to the elastic board 1 and going towards element 5A, the element 5A makes, together with the elastic board 1, a concave deformation, while the element 5B a convex deformation. As a result of the deformation, the resistance value of element 5A goes down, while that of element 5B goes up. Through calculation of difference in the shift of resistance value between element 5A and element 5B, the shift of resistance value is doubled, and outputted to represent the force applied to. In the mean time, the elements 6A and 6B receive only a torsional stress of a same direction, and there is no difference in the shift of resistance value between elements 6A and 6B. Therefore, only a force in the direction of coordinate axis of the first pair of strain detecting elements 5 is detected.
When the operating rod 2 is given at its end with a force in the direction P2 that is parallel to the elastic board 1 and going towards the middle point between element 5A and element 6A, the element 5A and the element 6A make a concave deformation, while the element 5B and the element 6B a convex deformation. As a result of the deformations, the resistance value of the elements 5A and 6A goes down, while that of the elements 5B and 6B goes up. The difference in the shift of resistance value between element 5A and element 5B of the first pair of strain detecting element 5, and the difference in the shift of resistance value between element 6A and element 6B of the second pair of strain detecting element 6 are calculated respectively to compare the differences, and the strength and the direction of the force applied to are detected and outputted. In the way described above, a force applied to the operating rod 2 is split into the elements of two coordinate axes, and the strength and direction are detected.
The conventional load sensors, however, carry with them tasks for improvement with respect to the ease of operation, in the following points.
Point 1 is that a load sensor is employed only as means for moving cursor on a display screen, and an execute switch is provided separately. An operator has to move his or her fingers to the execute switch every time when to make execute action.
Point 2 is that an operating rod is protruding for a certain length in excess of an overall contour shape of an appliance. This is a limiting factor in designing an appliance slim. Also, such an operating rod is readily affected by an external force, and could easily be deformed if the force is big.
Point 3 is that an expensive ceramic plate or enamel plate is used for the elastic board, and that the operating load-output voltage level relation of a load sensor is determined only by stiffness of the elastic board. Which means that the designing freedom is limited, and it is not easy to meet the diversifying requirements of customers swiftly and economically.